The RNLI are also locked into the search of this holy grail, unlike the Dutch who have adopted full planning for their boats. I myself am not convinced that the difference in rough weather performance is clear cut between the semi and full planing hulls.
Location: Flattop Islands KC Barnaby's Basic Naval Architecture of 1954 did not mention semi-displacement or semi-planing.
My personal view is that a Semi-Planing hull is one designed to lift substantially, and it's probably hard chined aft for maximum lift.
Most of us can associate to the type of vessel he is looking for, so why are you flipping his nose with a dozen of irrelevant notes on linguistics? Location: Milwaukee, WI Any hull that moves through the water produces waves.
BTW, it is completely possible to design a hull that is producing zero or negative hydrodynamic lift in the vertical plane, even if there will be dynamic forces acting on the hull as a result of movement. Location: Milwaukee, WI This is the first time you define what semi-displacement is for you. The regression methods mostly used for displacement speeds fail when it comes to speeds where dynamic lift is coming into play, and the empirical algorithms for planing are of little use in the intermediate speed range. Location: Milwaukee, WI Which comes to the original discussion, what is semi-displacement?
Location: Japan Not sure why stating basic facts is seen as a pissing contest by others?
One of my very good friends and I often debate this simple questions, what is a the definition of a semi-displacement hull. Originally Posted by baeckmo To be precise, the prefix "semi" per definition says that the boat is operated in such a way that its weight is carried 50 % by buoyancy, and 50 % by other means (normally, but not necessarily, by hydrodynamic lift), end of discussion!
If i were to have seen these lines and asked for my opinion, i would have suggested that it may be, but depending upon several other factors may be not too.
Pushing a boat through the water or riding a bit on top, both can be achieved in totally different ways, with both operating at the same speed. The person i referred to above, having this endless debate, simply because it amuses us, has been referred to here already. Laurent Giles' Woodpecker and Arthur Mursell of TT Designs and their Nelson range of pilot boats are all quoted as being the definitive examples. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Displacement Boat Plans J P and these are the letters that you see on the strategies of different sail cruiser. There are three main classifications of hulls; displacement, semi-displacement and planing. The vessel's run affects the vessels general performance and ability to attain certain speeds.
Semi-displacement or planing hulls can be identified by their buttock angle and shape of their run.
My thinking is that a formula along the lines of the one below could be used to establish whether a hull is limited to a hull speed or whether it is able to break free and continue accelerating in displacement mode e.g. The waterplane coefficient, Cw, could be used in place of angle of entry of bow, ideally just Cw of forward half of hull would be used. For hulls that do not exceed the critical k value, factors other than bow wave formation dominate drag, so the concept of relating the hull's maximum speed to the square root of its length is of little practical importance.
Alternatively you could take the opinion that there is no such thing as hull speed, hence trying to calculate it is pointless. Location: mallorca Displacement Hull Speed calculation Juan Baader the writer of the book?Cruceros y Lanchas Veloces? introduced a very simple way of Displacement hull speed calculation. Location: mallorca The displacement hull is a hull with narrow stern and the speed is limited to the waves the hull is producing.
Location: USA I tend to think it's probably impossible to come up with a single, simple equation that would be accurate enough for all hull forms and sizes.

The predictive value of such equation would tend to considerably diminish in extreme cases e.g. The problem seems to be that numerous factors affect R, and under different circumstances they don't always interact exactly in the same way with other factors. A more useful approach could be to find for each boat category of general size and form an equation that best describes empirical findings, and therefore would have a good predictive value for design purposes.
Location: Dubrovnik, Croatia If it would be that easy to calculate resistance what would be doing all these towing tanks and institutes.
Location: mallorca Using the R-Value formula it is very easy to calculate boat speed for Displacement hulls. Construction:  Construction is strip-planking on permanent plywood bulkheads, planking is sheathed outside with fiberglass and bulkheads are fillet and taped to the hull skin.
Construction Method and Materials: Strip-planking on permanent plywood bulkheads, planking is sheathed outside with fiberglass and bulkheads are fillet and taped to the hull skin. Lines & offsets, Two sail plans plus flying bridge outboard profile, General construction, Construction sections. Boston Previous Member   which is why I posted lines of the Downeast hull form, so folks could get a clear image of the type of hull commonly associated with a lobster boat. If your using a hull form of a traditional lobster boat people just might refer to is as such, specially if the top sides and sheer also resemble the layout. Location: Flattop Islands Once again Boston you have posted a question that could be addressed by writing 3-4 books.
From Massachusetts to Nova Scotia there are hundreds of versions of Downeast Lobster Boat hulls, some good , some bad, some indifferent.
Understand that these boats are built to make money, everything else is just gravy, if they don't make money they are put out to pasture. Originally Posted by Tad Once again Boston you have posted a question that could be addressed by writing 3-4 books.
A stretched version of White Pine will produce a very easily driven hull, if the weight is kept in check.
I would imagine that often the boats are loaded down with pots only a few times a year, at least the inshore boats, the pots spending most of the time in the water. I?m in the process of setting myself up for retirement and part of the plan is to upgrade my boat. I would like to be able to go across to Tasmania (120 - 450 nm depending on landfall chosen) or coastal hop up to the Great Barrier Reef and on to Darwin (longest leg I'd do around 450 nm). I do like the looks of White Pine but think it may be a little slow (her max is listed as 15 knots and I'd like to have some in reserve). The production boats available in Australia do not ?tick all my boxes? so I am seriously looking at building here (importing is not very attractive at current exchange rates) and we have 3-4 competent wooden boat builders where I live so this seems like my best option. If she's kept simple (light) you could expect 14 knots with about 120 HP at the prop and 12 knots with 73 HP. I got some feed back on onother forum that the down east hull is stable to a degree but in heavier seas its stability drops off fast. I like the way the beam narrows toward the stern and I also like the ?raised? floor and kitchen up in the main cabin area.
The head could be a fraction bigger so the ?shower? has a bit more room (I?d use this for hanging wet gear as well). Finally, last night I became aware of some select grade Alaskan Yellow Cedar planks (6? x 1? & 10? x 1?) that are available in near me, so I am thinking that this would be a good timber for planking the boat as I?m told it is light, strong and easy to work.
She has a round bilge clinker planked marine plywood hull with an open wheelhouse and a lower cabin with moderate flare forward and good size cockpit deck, strongly raked stem, transom stern and hinged timber slatted marlin platform. There is a very long way between these educated guesses and the real life finished boat, but the expectations are roughly in the range of possible.
The largest single weight in this boat will be the fuel load, so that capacity needs to be considered carefully. Location: Flattop Islands I'm also very jealous of the Yanmar engines available in Australia.

A 60' hull that displaces 53,400 pounds will require 44 Hp at the prop for 9 knots in flat water, no bearing looses, alternator drag, no current, wind, waves, no bottom growth, no appendages, etc. Originally Posted by Tad I'm also very jealous of the Yanmar engines available in Australia. His dismisses faster boats as only being suitable for the calm waters of the USA and the Riviera. There are many other factors that seem to be more important and can be incorporated into hulls of both types.
The towing tank archives are full of reports on these hulls, and there are certainly numerical attempts galore, so come on with the real stuff and skip the "semi********"!
And what do you call a hull that has 50 % aerostatic lift assistance from a "lighter-than-air" vessel? The problem with this analysis is that we are depending on different tools for the two (at least for the moment). The solent can be rough, short sharp chop at times, so a fully planning boat is out especially in the winter times. The "speed length ratio" or SL ratio is key in determining the practical speed potential of a hull. For the background to this thread see Humpless Planing in the Sailboat section of this forum. The small galley has space for a proper cast-iron wood range or the Bristol Dickenson diesel range.
No way they would be so popular among the fishermen if they were not well suited to it; not just the bay, but the open New England waters as well. I have recently joined the Royal Victorian Motor Yacht Club and this has given me the opportunity to look at a wide variety of boats and narrow down what I would like?..
I have looked at a locally built boat, a Cheviot 32, and it is lovely but just a bit to small for me, plus access to the bow is more difficult than I would like. Do you have any suggestions on how this design could be ?improved? to achieve (or exceed) these sort of targets while still meeting what I am after?
The lower cabin has a kitchenette, a separate toilet with wash basin and two bench seats that have been set up to convert to a basic double berth.
It may have been used on numerous occasions for this purpose but to say it was invented solely for this purpose is to dismiss all the real work that went into refining and exploring the semi-displacement hull form. This association of true planing vessels with being un-seaworthy for UK waters persisted for years (still persists?) and lead to thousands of hours being spent refining the idea of semi-displacement hulls, predominantly for the work boat market. However there are thousands of Pilot boat skippers and Lifeboat coxswains running their semi displacement hulls in all weathers, that are convinced that their boats are the way to go, and are not using these boats because they were fooled by the marketing strategy by some poor boat builder.
Generally good picket boat establishment strategies are created with careful consideration of these items.Similar models.
Brant rock ( well off the south shore ) has got so many buoys floating around it you could walk across em and its out in the middle of nowhere, definitely not protected water and we fixed plenty of boats that worked there.
I am not talking naval architecture again, I designed (looks at my gallery the 50' motor boat) it is a semi displacement she goes to 20 knots and do not plane. Fifty years of daily service in ports around the world would have rumbled these boats if they were nothing but an illusion. It uses a displacement that is suitable for the speed of decrease and I can t seem to find any 39 development strategies for vessels with displacement 50 25 39 full array. A semi-displacement, or semi-planing, boat is supported by a significant proportion of each.
However if you use ready-made strategies and just want to concentrate on the building of the boat you don't need to worry about such problems. It is extremely crucial to decide on the hull step for development of wooden boat Displacement Boat Plans.

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